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©2012 Aclara Technologies LLC
David W. Rieken, Zhixi Li, and Chris Fleck
Advanced Systems Research & DevelopmentAclara Technologies, LLC
St. Louis, MO, USA
VLF-band Power Line Channel
Sounding
©2012 Aclara Technologies LLC
Summary
VLF band (1-9 KHz)– Not regulated by the FCC
– Legacy AMI systems (e.g. TWACS, Turtle)
– Good signal propagation properties?
– Signal frequency is higher than mains, but still low enough to permit long distance comms
– Presents unique challenges to PLC because of low data rate and significant mains interference
Overview– VLF-band channel sounding
– Experimental setup
– Survey results
©2012 Aclara Technologies LLC
Channel sounding algorithm: signal model
3
©2012 Aclara Technologies LLC4
Channel sounding algorithm: transmitted signal
©2012 Aclara Technologies LLC5
Channel sounding algorithm: sounding procedure
©2012 Aclara Technologies LLC6
Channel sounding algorithm: periodic noise cancelation
©2012 Aclara Technologies LLC
Experiment setup
7
©2012 Aclara Technologies LLC
Experiment setup: transmission point
8
Laptop PC
DAQ
Filtered & unfilteredTx signals
Filtered Tx signal
Amplified Tx signal
LV line at premise
ZOH Tx signal
Anti-AliasingFilter
Power-lineCoupler
Tx Signal
PowerAmplifier
Anti-AliasingFilter
©2012 Aclara Technologies LLC
Experiment setup: receive point
9
Laptop PC DAQ
Filtered Rx signal
Anti-AliasingFilter
Power-lineCoupler
Rx signal
LV line at subst ation
©2012 Aclara Technologies LLC10
Analysis: convolution with sounding signal
Spreading signal so that it is orthogonal to mains makes detection in low SNR channels easy.
©2012 Aclara Technologies LLC
Survey results: Illinois site
11
0 1 2 3 4 5 6 7 8 9 10-80
-70
-60
-50
-40
-30
-20
f (kHz)
|H(f
)|2 (dB
)
1.3 mi1.8 mi3.3 mi5.4 mi7.2 mi9.7 mi
©2012 Aclara Technologies LLC
Survey results: Missouri site
12
0 1 2 3 4 5 6 7 8 9 10-80
-70
-60
-50
-40
-30
-20
f (kHz)
|H(f
)|2 (dB
)
1.1 mi3.4 mi25.2 mi
©2012 Aclara Technologies LLC13
SNR Analysis
©2012 Aclara Technologies LLC
SNR analysis: Illinois site (7.2 mi link)
14
0 2 4 6 8 10 6 7 8 9 10-120
-100
-80
-60
-40
-20
0
f (kHz)
dB
total SNR= 18.48 dB
TXNoise PSDChannel TransferRX
©2012 Aclara Technologies LLC15
SNR analysis: Illinois site (7.2 mi link)
Transmitter Power Max Data Rate
1 W 35.3 bps
5 W 176.5 bps
100 W 3.53 kbps
©2012 Aclara Technologies LLC
SNR analysis: Missouri site (25.2 mi link)
16
0 2 4 6 8 10 6,000 7,000 8,000 9,000 10,000-160
-140
-120
-100
-80
-60
-40
-20
0
f (kHz)
dB
total SNR= 29.52 dB
TXNoise PSDChannel TransferRX
©2012 Aclara Technologies LLC17
SNR analysis: Missouri site (25.2 mi link)
Transmitter Power Max Data Rate
1 W 448.7 bps
5 W 2.24 kbps
100 W 44.87 kbps
©2012 Aclara Technologies LLC18
Survey results: SNR by band
-20 -10 0 10 20 30 400
1
2
3
4
5
6
7
8
9
10
dB
Num
ber
of S
ites
1.5 - 2.5 kHz2.5 - 5 kHz5 - 10 kHz
©2012 Aclara Technologies LLC
Conclusions
19
Any VLF-band PLC system must– Accommodate a wide range of link strengths
– Leverage higher concentrator data rates than endpoint data rates
– Maximize system throughput, rather than instantaneous data rate
Analysis shortcomings– Sampling rate offset
– Time-varying channel IPR